Deregulation of lipid metabolism is the basis of some of the most common medical disorders in western populations, such as cardiovascular disease, fatty liver diseases, hyperlipidemia, and diabetes. The long-term goal in our laboratory is to gain a better understanding of whole-body lipid homeostasis in response to physiological, pathological, and pharmacological stimuli. In the previous cycle, we studied the role of the statin-induced murine miR-33 on hepatic lipid metabolism, HDL and bile secretion, reverse cholesterol transport, and atherogenesis. The current proposal includes two large sets of studies: first, to continue our studies on miR-33; and second, to introduce additional statin-induced miRNAs and study their role on hepatic metabolic control. In the first half of this proposal, we will use a novel liver-humanized mouse to continue our currently funded studies on miR-33. These mice overcome the critical limitations of traditional murine models, restoring hepatic human miR-33a and miR-33b, human miR-33 target specificity, and human-like lipoprotein profiles. The proposed studies will provide critical data on the consequences of therapeutic silencing of miR-33 in a human, functional liver. On the other hand, we present evidence that statins induce changes in the murine hepatic RISCome (RNA-induced silencing complex-associated mRNAs) in vivo. Among these changes, we focus on the miR-183/96/182 cluster target TCF7L2, and present evidence that the SREBP2-miR-183/96/182-TCF7L2 pathway mediates statin-stimulated hepatic glucose production in vivo. The translational relevance of this new conserved pathway is enhanced by the recently described diabetogenic effect of statins. We will test these new ideas using a combination of biochemical, cell biology, and in vivo techniques. Specifically, Aim 1 will test the functional role of human hepatic miR-33a and miR-33b on hepatic lipid metabolism, lipoprotein secretion, and atherogenesis. Importantly, the unique liver-humanized mice will also allow us to test for the first time the contribution of miR-33b to diet-induced fatty liver and hepatic insulin resistance. Aim 2 will define the functiona role of miR-183/96/182 on hepatic and whole-body glucose homeostasis, by determining the contribution of each miR to hepatic glucose production, defining the mechanism by which the miR cluster and TCF7L2 regulate gluconeogenesis, and studying whether the levels of miR-183/96/182 and their functional targets are altered in murine models of altered glycemic control. The insights from these studies will fill a current gap of knowledge in pathophysiological hepatic metabolic control, and may uncover novel pharmacological targets to manage liver diseases, diabetes, and cardiovascular risk.